The present application claims priority under 35 U.S.C. xc2xa7 119 of German Patent Application No. 199 12 500.7, filed on Mar. 19, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a process and apparatus for determining properties of a traveling material web, e.g., a paper web in a paper machine.
2. Discussion of Background Information
When manufacturing webs, for example, paper webs, an effort is made to obtain the greatest possible amount of information about the material web being created, in order to have the option of intervening deliberately in the manufacturing process.
It is known to take spectroscopic measurements using electromagnetic radiation in the IR range on a paper web in a paper machine to determine parameters which are relevant for the process from the interaction of the IR radiation with the paper web information. To do so, traversing measurement heads, i.e., running crosswise (transverse) to a web travel direction, are used which operate with multiple discrete wavelengths in order to inspect the paper web, e.g., with regard to moisture, basis weight, opacity, or content.
The problem with such traversing systems is the high production speed in modem manufacturing machines which, in the case of paper machines can be, e.g., on the order of 2,000 m/min. With the known traversing measurement systems, it is impossible at such high process speeds to obtain cross-direction profiles or so-called xe2x80x9ctime-shifted cross profiles,xe2x80x9d because the distribution of the respective pertinent parameters across the width of the material web cannot be determined or can be determined only with insufficient accuracy. Furthermore, the large dimensions of traversing systems are a disadvantage because they can only be used at very few locations of the machine, for example, only at the end of a paper machine.
It is also known to evaluate continuous IR spectra using different mathematical processes, in which the measurements are taken at only one location and are frequently taken with complex, expensive instruments, such as FTIR spectrometers.
Known devices and/or processes are described, e.g., in U.S. Pat. No. 4,098,641, EP-0 137 696, WO 98/36264, WO 95/08019, WO 93/15389, and WO 95/31709, the disclosures of which are expressly incorporated by reference herein in their entireties.
The present invention provides the simplest and least expensive capability for determining the properties of a traveling material web which, in particular, allows quick cross-direction profiles to be determined at selected places on the material web.
The present invention includes a plurality of measuring points on the material web that are simultaneously illuminated and imaged through at least one optical device on one detection surface divided into multiple individual detection surfaces of at least one detector.
According to the invention, multiple areas of the material web can be simultaneously inspected without contact. The division of the detection surfaces of the detector makes it possible to process or evaluate the signals generated by the imaging of the measuring points on the detection surface of the detector separately at first by measuring point and subsequently to combine them into an overall image of the material web. According to the invention, for each measurement, a partial area of the material web containing the measuring points is imaged on the detection surface of the detector. Therefore, a snapshot of the material web is obtained with each measurement. Because measurements are taken simultaneously at all measuring points according to the invention, the result can be used for a quick control and/or adjustment of the manufacturing process immediately after the measurement. In combination with sufficiently rapid processing devices, it is therefore possible to achieve continuous process monitoring with the capability of immediate correction. A quick adjustment prevents or minimizes the production of rejects and results in fewer quality fluctuations. Moreover, the quick intervention allowed by the process according to the invention can be particularly advantageous in the case of material changes or generally when changing over to another product.
According to the invention, the material webs can fundamentally be inspected with regard to every property by which the interaction of electromagnetic radiation with the material web is influenced. In manufacturing paper, e.g., the moisture content or moisture, basis weight, opacity, fiber orientation, thickness, surface properties, type and/or distribution of contents, etc., are parameters with regard to which an inspection of the paper web that is being produced or the finished product is of interest. The capability of inspecting in rapid succession each of several areas of the material web simultaneously, makes it possible, e.g., to measure the moisture of the paper web immediately after the press part of a paper machine, in order to adjust a vapor bubble box of the dry part on the basis of the measurement results.
Of course, the present invention is not limited to paper machines or to specified positions in a machine. Instead, properties of other material webs, e.g., any chosen fiber material webs, including cardboard webs as well as textile webs, which are of interest can be determined at any chosen position of the manufacturing machine.
When, according to an exemplary embodiment of the invention, the measuring points are located along a substantially straight line, it becomes possible for the material web to be line scanned using the detector and/or the optical device. In this regard, the material web can be illuminated in such a way that the straight line formed by the measuring points extends at least substantially cross-wise (or perpendicularly) to the web travel direction (i.e., the measuring points are substantially illuminated through the optical fibers). In this way, current cross-direction profiles of the material web can be obtained, in order to determine the distribution of the parameters across the width of the material web.
The use of electromagnetic radiation in the IR range to illuminate the measuring points according to another exemplary embodiment of the invention makes it possible to operate IR spectroscopy at the measuring points. This radiation is particularly appropriate for determining the moisture of paper webs. For example, radiation in the range of approximately 0.1 xcexcm to 40 xcexcm can be used. A preferred wavelength range is in the near-IR range and includes, e.g., wavelengths between approximately 1.0 xcexcm and 2.5 xcexcm.
The material web can be illuminated using appropriate sources of IR radiation in order to take reflection measurements at the illuminated measuring points, with the measurements preferably taken in diffuse reflection. It is also possible to transilluminate the material web with IR radiation and to take transmission measurements by detecting on the detector any radiation that penetrates through the material web at the respective measuring points.
According to another exemplary embodiment of the invention, each measuring point can be imaged using an optical fiber.
Using optical fibers, the radiation originating from the measuring points can be guided to any chosen place, particularly one that is spatially separated from the material web. Thus, the space required for the invention at the material web can be minimized. The process according to the invention can therefore be carried out even when space is limited and consequently, in principle, can be used at any position on a machine for manufacturing the material web. Consequently, the space available for the detector or the devices adjacent to the detector is not limited. Therefore, the invention also makes it possible to take measurements, e.g., immediately after the servo components of the machine which are used to influence manufacturing. In that way, the control systems for the process are minimized.
Instead of optical fibers, it is also possible to use a respective slit-shaped screen arrangement for illuminating the measuring points, such that the each measuring point can be imaged on the detector detection surface, and the screen arrangement can be provided with an optical device connected before or after it.
Particularly informative results can be obtained when, according to another embodiment of the invention, different wavelengths and/or wavelength ranges of the electromagnetic radiation originating from the measuring points can be detected on the detector in chronological succession, e.g., periodically.
In one example, the wavelengths 2.05 xcexcm, 1.95 xcexcm, and 1.83 xcexcm are detected successively on the detector. Particularly when determining the moisture of paper webs, such measurements provide informative results and are particularly advantageous in the low-moisture range. In any application, it can be ensured according to the invention that the only radiation that is detected on the detector is that from which information can be obtained about the parameters that are of interest for the material web.
For measurements related to wavelength, a filter unit including a plurality of filter elements having different wavelength selectivity can be connected before the detector. The filter elements can be distributed in the circumferential direction on a rotating disk, to be brought into the radiation path in chronological succession by the rotation of the disk, which operates in the manner of a chopper. Such a filter unit or chopper disk allows periodic selection of the respective wavelength ranges to be detected.
At least one filter element can be constructed as a graded filter in one variation of the invention. In this way, wavelengths located in succession within a continuous range of the radiation originating from the measuring points can reach the detection surface of the detector.
According to another embodiment of the invention, at least some measuring points are each imaged on exactly one individual detection surface of the detector.
The unique allocation of one measuring point to a respective individual detection surface of the detector, which is also known as a pixel, makes optimum use of the maximum position resolution that is achievable using the respective detector.
It is also possible according to the invention to image at least some measuring points simultaneously on several individual detection surfaces of the detector.
The allocation of single measuring points to multiple individual detection surfaces which, in this way, are combined to some extent to form a xe2x80x9csuperpixel,xe2x80x9d minimizes detector noises and improves the signal-to-noise ratio of the measurements. The individual detection surfaces or pixels allocated to one measuring point can be combined or connected together into a xe2x80x9csuperpixelxe2x80x9d either as part of signal processing or evaluation or using hardware.
According to another embodiment of the invention, one or several radiation sources can be used for illumination and moved as a whole system transverse to the web travel direction or the optical device can preferably be moved relative to the material web cross-wise or approximately perpendicular to the web travel direction, with the movement preferably being periodic and, e.g., made with a small amplitude compared with the width of the material web. To do so, the radiation sources and at least the light entrance areas of the optical device, e.g., the sections of optical fibers which are each provided with one entrance surface, can be supported on a measurement crosspiece extending cross-wise to the web travel direction over the width of the material web. The crosspiece can be moveably mounted in the longitudinal direction.
With a device that is moveable cross-wise to the material web, every point on the material web can be reached. In particular, as a function of the speed of the movement and the read-out of the detector signal, continuous inspection of the material web can be achieved.
According to another embodiment of the invention, signals supplied by the detector may be transmitted to a process control system for control and/or regulation of the manufacturing process of the material web.
In the process control system, the signal, which may optionally be preprocessed in an evaluation unit connected before the process control system and prepared in a computer using appropriate algorithms, can be compared with prespecified target values for the individual parameters. Based on the results of the comparison, an intervention may be made on the process control if necessary.
The present invention also includes at least one radiation source for illuminating the multiple measuring points on the material web, at least one detector having a detection surface divided into multiple individual detection surfaces, and at least one optical device for imaging the measuring points on the detection surface of the detector.
The present invention is directed to a process for determining properties of a traveling material web. The process includes simultaneously illuminating a plurality of measuring points on the material web with electromagnetic radiation, and imaging, through at least one optical device, the plurality of measuring points on one detection surface of at least one detector.
According to a feature of the invention, the one detection surface may be divided into a plurality of individual detection surfaces. Further, the material web can include a paper web.
In accordance with another feature of the invention, the process can also include arranging the measuring points to lie along a substantially straight line extending at least essentially cross-wise to a web travel direction.
According to still another feature of the instant invention, the electromagnetic radiation can be within the IR range. Further, the electromagnetic radiation can be within the near-IR range, and the electromagnetic radiation may have a wavelength range of approximately 1.0 to 2.5 xcexcm.
In accordance with a further feature of the present invention, the imaging of the plurality of measuring points can utilize light reflected by the material web at the plurality of measuring points.
According to a still further feature of the invention, the imaging of the plurality of measuring points may utilize transilluminated light at the plurality of measuring points, and the process can further include taking transmission measurements of the transilluminated light at the plurality of measuring points.
In accordance with another feature of the invention, the imaging of at least some of the plurality of measuring points may include transmitting optical data through an optical fiber.
According to another feature of the present invention, the imaging of at least some of the plurality of measuring points can include imaging through a slit-shaped screen arrangement having an optical device coupled one of before and after the screen arrangement.
Further, the imaging of at least some of the plurality of measuring points can include detecting at least one of different wavelengths and wavelength ranges of electromagnetic radiation originating from the measuring points on the detector. The at least one of different wavelengths and wavelength ranges of electromagnetic radiation originating from the measuring points can be successively detected. Further still, the at least one of different wavelengths and wavelength ranges of electromagnetic radiation originating from the measuring points can be periodically detected.
Still further, at least one discrete radiation spectrum detected on the detector may include the wavelengths of approximately 2.05 xcexcm, approximately 1.94 xcexcm, and approximately 1.83 xcexcm.
The process can also include selecting at least one of individual wavelengths and wavelength ranges of the radiation to be detected with at least one filter unit. The at least one filter unit can be positioned between the at least one optical device and the detection surface.
In accordance with another aspect of the instant invention, the measuring points may be illuminated by at least one of approximately dot-shaped and at least one line-shaped radiation source.
According to still another aspect of the present invention, the detection surface can include a plurality of individual detection surfaces, and at least some measuring points can be imaged on exactly one individual detection surface. Still further, the detection surface can include a plurality of individual detection surfaces, and at least some measuring points can be imaged on a plurality of individual detection surfaces.
At least one of at least one illuminating radiation source and the at least one optical device can be movable relative to the material web. The at least one of at least one illuminating radiation source and the at least one optical device can be movable the cross-wise to a web travel direction. The movement of the at least one of at least one illuminating radiation source and the at least one optical device may be periodic, and can have an amplitude substantially equal to a distance between measuring points.
In accordance with a further aspect of the invention, the process can further include transmitting signals from the detector to a process control system adapted for control and/or regulation of a manufacturing process of the material web. Signal preparation can occur before transmission to the process control system.
The present invention is directed to a device for determining properties of a traveling material web. The device includes at least one radiation source for illuminating a plurality of measuring points on the material web, at least one detector having a detection surface, and at least one optical device for imaging of the measuring points on the detection surface of the at least one detector.
According to a feature of the invention, the detection surface comprises a plurality of individual detection surfaces. The material web can include a paper web.
In accordance with another feature of the invention, the at least one radiation source can include at least one of a plurality of approximately dot-shaped radiation sources and at least one approximately line-shaped radiation source.
According to still another feature of the instant invention, the at least one optical device can include a plurality of optical fibers, and each of the plurality of optical fibers may be assigned to a measuring point. An entrance surface of each of the plurality of optical fibers can be positioned directly adjacent to the material web. An entrance surface of each of the plurality of optical fibers may be positioned directly adjacent the assigned measuring point. The plurality of optical fibers may include moisture-free quartz and may have a diameter of approximately 200 xcexcm. Emergent sides of the plurality of optical fibers may be combined into an emergent surface that is at least approximately adapted to a shape of the detection surface. The emergent surface can be slit-shaped.
In accordance with a further feature of the invention, the at least one detector can include a line detector, and the detection surface may be strip-shaped. The detection surface may be divided into a plurality of pixels.
The device can also include a filter unit coupled before the at least one detector. The filter unit can include a plurality of filter elements having different wavelength selectivity. The plurality of filter elements can be successively positioned into an optical path. The filter elements may be circumferentially distributed on a rotatable disk.
Further, the at least one radiation source and light entrance surfaces of the at least one optical device may be combined into a measurement unit arranged to extend across at least substantially an entire width of the material web and cross-wise to a web travel direction. The measurement unit may be movable cross-wise to the web travel direction.
The present invention is directed to a device for determining properties of a traveling material web. The device includes at least one radiation source for illuminating a plurality of measuring points on the material web, at least one detector having a detection surface having a plurality of pixels, and at least one optical device for imaging of the measuring points on the detection surface of the at least one detector. The at least one optical device may include a plurality of optical fibers, wherein each optical fiber can be assigned to a respective measuring point. The plurality of optical fibers can include entrance surfaces positioned adjacent the respective measuring point, and emergent sides coupled to provide images of the measuring points on the detection surface. A filter device can be positioned between the emergent sides and the detection surface.
According to an aspect of the invention, the filter device may include a rotatable disk including circumferentially spaced filters. Between the spaced filters, the rotatable disk can be opaque to radiation.
In accordance with yet another feature of the instant invention, some of the plurality of optical fibers are associated with only one pixel, and other of the plurality of optical fibers are associated with more than one pixel.